In an exemplary distributed power system, a single, relatively high power supply converts input line voltage to a semi-regulated voltage which is then supplied to a multitude of individual "point-of-load" power supplies located at the loads to be served. Power is usually distributed to the point-of-load supplies along the back-plane of a modular assembly, and the relatively high power supply is thus often referred to as a "back-plane" power supply. Typically, the back-plane supply has its input derived from a prime power source which may exhibit substantial voltage transients. The back-plane supply must continuously supply the regulated power to the point-of-load supplies despite these normal transient disturbances. In a military application of distributed power, for example, the prime power is often specified to be that defined by military standard MIL-STD-704D. The steady-state input voltage defined by this standard is in the range from 250 to 280 Vdc. However, under this standard, normal dc operation is defined as including an envelope of voltage transients that can make the effective input voltage vary between 125 and 475 Vdc. Unfortunately, however, high-frequency power supply topologies which meet the aforementioned input voltage range requirement while still maintaining high-efficiency, steady-state operation have been heretofore unavailable. In particular, as the lower limit of the voltage range requirement decreases, efficiency decreases. For example, in a resonant circuit topology, which advantageously enables operation at high frequencies and hence the use of small circuit components, the decrease in efficiency is primarily due to the fact that peak circulating currents in the resonant components and primary-side active devices are determined by the minimum voltage requirement. Since the peak circulating currents are higher for a lower voltage requirement, and the circulating currents remain relatively constant for voltages above the minimum voltage requirement, conduction losses increase as the minimum voltage requirement decreases. Alternatively, to minimize losses, components can be made larger, but at the expense of power density. Therefore, it would be desirable to provide a high-density power supply for supplying a regulated output voltage at high efficiency even for an input voltage which may exhibit substantial transients. To this end, it would be desirable to employ a resonant converter exhibiting substantially lossless switching, such as by the zero-voltage switching technique described in "A Comparison of Half-bridge Resonant Converter Topologies" by R. L. Steigerwald, IEEE Transactions on Power Electronics, April 1988, pp. 174-182, which is hereby incorporated by reference, while also providing means for minimizing active device conduction losses, despite substantial input voltage transients.